The present invention generally relates to the field of acceleration fuel enrichment systems for an engine. More specifically, the present invention relates to the determination of the pulse width durations for acceleration enrichment pulses provided in such systems and the termination of the development of the acceleration enrichment pulses in such systems.
Many types of prior acceleration enrichment systems are known wherein during an increase in throttle position additional fuel is supplied to the engine whereas a substantial time after the transient increase in throttle position a steady state or base fuel control circuit provides engine fuel in accordance with the final or steady state throttle position. Typically the base fuel control circuit supplies base fuel control pulses which are synchronous with predetermined engine cylinder piston positions. In essence, acceleration enrichment systems are concerned with providing additional engine fuel during engine throttle position transients so as to improve the engine acceleration response by suppling the extra fuel needed during acceleration.
Some prior acceleration fuel enrichment systems respond to an engine acceleration transient by merely extending the fuel control pulse durations of the base engine synchronous fuel control pulses that are provided by the steady state fuel pulse control circuit. These acceleration enrichment systems typically do not perform in a satisfactory manner in that they do not react fast enough to an engine throttle position increase to provide additional fuel when it is needed by the engine. The result is hesitation of the engine during acceleration because of an excessively lean fuel mixture. Some other acceleration fuel enrichment systems attempted to solve this problem by developing asynchronous fuel control pulses which immediately added fuel to the engine upon the detection of a substantial increase in throttle position. Several of these type of acceleration fuel enrichment systems utilized engine control microprocessors to control not only the additional asynchronous acceleration enrichment pulses utilized for fuel control but also to calculate and provide the synchronous base fuel control pulses used for engine fuel control.
In the above described prior acceleration enrichment systems, after a lack of further increase in the throttle position has been determined either the acceleration enrichment is abruptly terminated or it is terminated acccording to a predetermined decay. Some additional acceleration enrichment after the throttle position has ceased to increase is typically provided to compensate for the fact that the engine may still have not arrived at a steady state condition. This explains why this additional enrichment is decayed as a function of time. The duration of the acceleration enrichment pulses provided during this decay of acceleration enrichment is typically predetermined based on engine operational parameters or their rate of change as determined during the increase of engine throttle position. In addition, the length of time during which acceleration enrichment decay pulses are provided is typically either a fixed time period, a time period determined in accordance with a predetermined number of engine revolutions, or a time period dependent upon engine operational parameters or their rates of change which exist during the increase of engine throttle position and engine manifold pressure produced in response to an increase in throttle position.
While some of the acceleration enrichment systems corresponding to the those described above perform fairly well, these systems do not optimize fuel delivery after the initial transient because they may provide either an excessive or insufficient amount of engine fuel. This is because the durations of the acceleration enrichment pulses provided after the initial increase in engine throttle position are typically determined by variations in throttle position and/or engine manifold pressure which occur prior to the acceleration enrichment decay characteristic. In other words, after the initial rising transient provided in response to throttle depression, the durations of acceleration enrichment pulses are determined in accordance with the variations of the engine operational parameters of throttle position and engine manifold pressure which preceded the acceleration enrichment decay characteristic. Thus the acceleration enrichment decay characteristic is typically not a function of current engine conditions and therefore this decay characteristic does not properly reflect the actual amount of acceleration enrichment which is required by the engine after the initial throttle position transient. In addition, the fact that some prior acceleration enrichment systems terminate the acceleration enrichment decay after a predetermined time interval based on either the passage of a fixed period of time or the attainment of a predetermined number of engine revolutions, also makes the time during which acceleration enrichment decay occurs nonrepresentative of the primary engine operational parameter of engine manifold presure which exists after the initial acceleration transient which was caused by depression of the engine throttle.